The major objective of the proposed research is to elucidate the molecular mechanisms governing periodic expression of specific mRNAs during the cell cycle. The primary focus of the studies described herein is to understand the transcriptional and post-transcriptional regulatory events controlling the accumulation of human histone mRNA during the S phase of the HeLa cell cycle. Additional studies, employing the methodologies developed for the analysis of histone gene expression, will be pursued discover those processes controlling the cell cycle specific expression of other cellular genes. The proposed research will be conducted according to the following course. First, the expression of several individual genes encoding each of the histone subtypes will be analysed in vivo to identify those that code for the most abundant cell cycle regulated mRNAs. Second, in vitro studies of both the transcriptional and post-transcriptional mechanisms which control the accumulation of each histone mRNA will be conducted in soluble extracts from synchronized HeLa cells. Current studies of the pHu4A histone H4 gene (see below) provide a useful paradigm for the analysis of other cell cycle regulated histone genes. Thus, these studies will focus on the identification of both nucleotide sequences and protein factors which are involved in the expression of histone genes in vitro. Third, in vivo studies employing either transiently or stably transfected histone genes will be pursued to demonstrate that the nucleotide sequences which are important for histone gene transcription in vitro are also utilized in vivo. This methodology will also be employed to determine whether specific sequences in histone mRNA provide a signal for its rapid and specific degradation after the inhibition of DNA synthesis. Fourth, similar experiments will be conducted to identify those events controlling the cell cycle specific expression of other cellular genes. The initial emphasis in this area will be to gain insight into the dramatic transcriptionsl regulation of the human HSP 70 gene we have observed during the HeLa cell cycle. It seems apparent that studies of this type can generatecrucial information concerning the regulation of specific genes, as well as provide an avenue toward an increased understanding of general processes required for progression through the cell cycle.